Protective device permitting more specially the use of probe in large diameter wells

ABSTRACT

The present invention relates to a device and method for using a logging probe of small diameter with resect to a well in which it is to operate. The device of the invention is characterized in that it includes a widener for widening the diameter of said probe.

This is a continuation of application Ser. No. 069,174, filed July 2,1987, now U.S. Pat. No. 4,929,915.

BACKGROUND OF THE INVENTION

The present invention relates to a protective device for widening andenlarging the effective active surface for probes or instruments used inlogging measurements and methods using this device.

The present invention allows logging measurements to be made in a largediameter well using a logging probe adapted for operation in smalldiameter holes.

Of course, the notion of large diameter of the hole is to be consideredrelatively to the dimensions of the probe.

Furthermore, the present invention protects the probes or instruments orthe sensitive parts thereof against the lateral and/or longitudinalmechanical actions.

When measurements are made, because of jamming, cave-ins in the well orhigh thrust forces (several tens of tons even hundreds of tons) ortorsional stresses communicated to the drill pipe string, the probesand/or the tools are subjected to actions likely to destroy themirremediably particularly some of these instruments which are generallyvery expensive.

The probes generally used in well logging have standard diameters (forexample 85 mm or 92.5 mm).

These probes allow measurements of good quality to be made in holeshaving diameters not exceeding a maximum value. Thus, for probesmeasuring the resistivity of the geological formation, the ratio betweenthe diameter of the hole and the diameter of the probe should not exceedsubstantially 3.5. This is due to the phenomenon called "hole effect" bya man skilled in the art and will be explained hereinafter.

By applying a device of this invention to the probe, the presentinvention allows good quality measurements to be made with a smalldiameter probe. It becomes then possible, in accordance with the presentinvention, to increase the range of well dimensions in which a givenprobe may be used.

SUMMARY OF THE INVENTION

Thus, the present invention provides a protective device which allowsthe use of a logging probe of small diameter with respect to the well inwhich the probe is to operate. This device includes means for wideningthe effective diameter of said probe i.e. the active surface generatingan electric or electromagnetic field.

This device may include a casing surrounding at least a sensitive partof said probe.

This casing may define a substantially sealed space about the sensitivepart of said probe.

This sealed space may be filled with an electrically non conductingmaterial such as distilled water or oil.

The protective device may include corresponding electrodes and means forelectric connection between the electrodes of said probe and those ofthe protective.

The electric connection means may include an electric ring.

The protective has means for centering the casing, which may essentiallyinclude rings.

The centering means may include fixing means.

The device of the invention may include spacers for positioning at leastsome of said rings and it may include electrically non conducting wallsinserted between at least two electrodes of the probe.

The device of the invention may be a solid assembly.

The device of the invention may be adapted to an induction orparticularly a focused resistivity measuring probe or to a probecombining resistivity and induction measurements.

The device of the invention may very advantageously further provideprotection for said probe and more precisely of those fragile partswhich generally correspond to the active or sensitive zones of theprobe.

Furthermore, the present invention provides a means for fixing a probeor instrument cover.

By probe or instrument cover it is meant any element capable ofisolating the probe or instrument over at least a part thereof. Thiscover may for example be a local screen or a complete casing.

This cover may serve for example either for protection from outsideinfluences, such as foreign bodies, physical (mechanical, thermal . . .) or chemical stresses, or for selecting influences coming from or goingtowards the probe, such as those of gamma rays focused through a windowand detected through another.

This fixing means is characterized in that it includes at least onehousing cooperating with at least one arresting element and furtherincluding an assembly of securing pieces retained by the arrestingelement and having at least two stops cooperating with the arrestingelement for securing the casing of the probe.

The housing may be a groove formed in the probe and the arrestingelement, such as a system of two half moons, which form a collar for theprobe.

One at least of the arresting elements may cooperate with two stops ofthe securing piece assembly.

The securing piece assembly may include an additional adjusting piecefor moving the cover relatively to the probe.

The cover may be a cover protecting at least a sensitive part of theprobe.

The cover may be a device for widening at least the sensitive part ofthe probe.

The securing means may include at least two grooves each cooperatingwith an arresting element and each forming a collar for the probe andthe securing piece assembly may cooperate with at least these collars.

The cover may include at least one window adapted for letting throughactive measurement and/or intervention members of the probe orinstrument.

The present invention also provides a method for using a probe of smalldiameter relatively to a well for carrying out measurements therein. Inthis method, said probe is equipped with a protective device, saiddevice being adapted for transmitting the signals emitted by the probewithout too much damping.

The present invention also provides a method for protecting at least asensitive part of a probe or instrument from mechanical traction and/orcompression an/or twisting actions. In this method, said probe isequipped with a cover, said cover being adapted for transmitting themechanical forces outwardly of the sensitive part without transmittingtoo much stress to said sensitive part. The cover is adapted to transmitthe signals emitted and/or received by said probe without too muchdamping.

The device, the securing member and the methods of the present inventionmay be applied to a well formed in a geological formation particularlyfor carrying out oil prospection.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be better understood and its advantages willbe clear from the following description of different embodiments, whichare in no wise limitative and which are illustrated by the accompanyingFigures in which:

FIG. 1 illustrates a bare probe, placed in a large diameter hole,

FIG. 2 shows a probe equipped with a probe protective device,

FIGS. 3 and 4 show a particular embodiment of the protective devices,

FIGS. 5 and 6 show two particular embodiments of the protective devicesadapted for example to induction probes,

FIGS. 7 and 8 concern two particular embodiments of protective devicesadapted to probes having electrodes, for example for measuring theresistivity of a geological formation,

FIG. 9 shows a probe widener adapted to a probe having electrodes andable to carry out induction measurements,

FIGS. 10 to 13 illustrate different embodiments of the electricalextension between the electrodes of the probe and the electrodes of theprotective device, and

FIG. 14 shows a probe equipped with a cover for protection againsttwisting forces.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a sectional view of a well 1 bored in geological formation2.

Reference 5 designates the walls of the well and reference 4 themeasuring probe.

The diameter d of the measuring probe 4 is much less than the diameter Dof the well. Thus, a large number of the electric or electromagneticfield lines do not pass into the geological formation and are shortcircuited through the mud which fills the free space 3 between probe 4and the walls of well 5. Reference 6 designates the outer wall of probe4.

The present invention proposes fitting a probe protective device 7 (FIG.2) to the probe 4.

In FIG. 2, the protective device includes a casing 8 of cylindricalshape whose diameter T is greater than that of the probe (d) and lessthan that of the well (D).

In FIG. 2, the cylindrical casing 8 is held in position coaxially withrespect to the probe by a dividing wall in the form of a ring having twohalf shells 9 and 10 joined together by screws 11 and 12 which, whentightened, hold it on the probe. Other systems for fixing the dividingwalls on the probe may be envisaged without departing from the scope ofthe present invention. For example, the dividing wall may have the shapeof a ring formed of a single piece whose inner diameter is slightlygreater than that of the probe. This ring 15 (FIG. 11) may have a radialthread 13 (FIG. 11) with which a screw 14 may cooperate which, whentightened, holds the ring on the body of probe 4.

FIGS. 3 and 4 show the case where the protective device is a solidassembly. This assembly may include a casing containing a fillingmaterial, or be simply in one piece, or a stack of rings.

In FIG. 3, the probe 4 is a probe for carrying out resistivity andinduction measurements. This probe has five rows 16, 17, 18, 19 and 20of active elements. Each of these rows includes several electrodes 16a,16b, 16c . . . in the form of inserts disposed about a circle inscribedon the body of probe 4.

The device 7 includes a solid material 21 such as an electricallyinsulating epoxy resin.

Device 7 has on its outer wall 22 electrodes 161a to 161d also in theform of inserts.

When electrodes 16a, 16b, 16c, 16d . . . are connected togetherelectrically, the electrodes 161a, 161b . . . of the same row will alsobe connected electrically together and it will be sufficient for onlyone of the electrodes of the protective device to be connectedelectrically to an electrode of the homologous row 16 of the probe. Thisis shown by the electric connections 162, 172, 182, 192 and 202respectively for rows 16, 17 18, 19 and 20 in FIGS. 3 and 4.

The inserts in the same row of the device are then connected together,however at least two inserts of the same row are not connected together,so as not to form closed circuits and cause the creation of currentloops. This is illustrated in FIG. 13 which clearly shows that there isno electric connection between inserts 161e and 161a, whereas electricalconnections 163a, 163b, 163c, 163d, 163e do exist.

Such a configuration allows the induction field to pass through theprotective device 7 of probe 4 without too much attenuation i.e. theactive surface of the probe is enlarged to reduce attenuation ofelectric and electromagnetic fields caused by the presence of conductivematerial between the probe and the inner wall of the well casing.

The protective device is held in position on the probe by positioningand holding rings 23 and 24 (FIGS. 3 and 4).

FIG. 4 shows the case of a device 7 for a probe 4 forming a solidassembly fitted to a probe for measuring the resistivity of theformation which does not make induction measurements. Generally, thistype of probe has two electrodes in the form of continuous rings, placedat different heights in the probe.

The probe of FIG. 4 has five annular electrodes identified by thereference numerals 25, 26, 27, 28 and 29.

The protective device has five annular electrodes analogous to thepreceding ones and respectively, identified by the reference numerals25a, 26a, 27a, 28a and 29a.

Each of these electrodes is connected to the corresponding electrode ofa probe by electric connections 252, 262, 272, 282 and 292.

These the connections may include metal rods possibly threaded and/orhave pushers, such as those illustrated in FIGS. 12 and 13.

The protective device is fixed to the probe by rings 23 and 24.

In the case of FIG. 4, the probe is extended by the lower tubularelement 30 and it is therefore necessary for the protective device to bepierced with a through bore.

In the case of FIG. 3, the protective device 7 could be closed at itslower part and include the lower end 31 of probe 4.

The probes of the different FIGS. 3 to 9 are shown suspended from acable 32, but it is obvious that without departing from the scope of thepresent invention, the probes may be fixed to the end of a tube such asa drill pipe string, or in the case where they themselves correspond toa portion of a tube. The following patents: FR-A-2 544 013; FR-A-2 547861; FR-A-2 564 894; U.S. Pat. No. 4 457 370 and U.S. Pat. No. 4 570 709illustrate examples of use in which the present invention applies.

In the case where probe 7 of FIG. 3 is not a probe ensuring bothresistivity and induction, but simply an induction measurement probe, itwould not include the rows of electrodes 16, 17, 18, 19 and 20 and thewidener would have neither electrodes 161a . . . 161d nor conductors162, 172, 182, 192 and 202. Thus, the widener could be formed of afilled assembly, possibly solid, made from an electrically nonconducting material such as an epoxy resin.

FIGS. 5 and 6 show two other embodiments of the protective device fittedto induction probes.

In the case of FIG. 5, reference numeral 33 designates the sensitivepart or active zone of the induction probe which is placed at the end ofa cable 32 and is not extended by a tubular element 34, as is the casefor the probe of FIG. 6, this tubular element being possibly anotherprobe or another member.

In the case of FIG. 5, the protective device has a casing 35 surroundingthe lower end 36 of the probe. This casing is made from an electricallynon conducting material and may be made from a non conducting epoxymaterial.

Of course, it is sufficient simply for part 37 of casing 35 adjacent theactive zone 33 of probe 4 to be made from an electrically non conductingmaterial.

Thus, in the case of FIGS. 5 and 6, the endmost parts 38, 39 and 40 ofdevice 7 may include metal.

The casing of device 7 is centered by dividing walls 41 and 42, in sofar as the embodiment of FIG. 5 is concerned, end walls 43, 44, 45 and46 in so far as the embodiment of FIG. 6 is concerned. Of course, atleast the dividing walls adjacent the active zones 33 of the probe aremade from an electrically non conducting material. These dividing wallsmay be secured to the probe in different ways, as shown particularly inFIG. 2.

Furthermore, without departing from the scope of the present invention,the dividing walls may be secured to the protective device instead ofbeing secured to the probe itself.

The following description gives one non-limitative embodiment of theendmost parts 38 and 39 of the protective devices, these endmost partsbeing adapted for fixing the devices to the probe.

In the particular example shown in FIGS. 5 and 6, the casing 35 of thedevice ends at its upper part (relatively to the Figures) in a metalpiece 47 on which the electrically non conducting part of the casing isfixed during molding, for example by bonding.

This metal piece 47 ends in a tapped portion 48 which cooperates with athreaded portion 49 of an intermediate piece 50. This intermediate piececooperates with a securing piece 51 by means of a screw thread system52.

The intermediate and securing pieces include respectively stops 53 and54 which encase an arresting element, such as a system of two half moons55, having a collar 56 which cooperates with a groove 57.

Thus, clamping of the intermediate piece 50 and the securing piece 51hold and position the protective device.

The lower end 40 of the embodiment shown in FIG. 6 is securedsubstantially in the same way and has a metal part 47a which is securedto the non metal part of the casing. This part cooperates with anintermediate piece 50a which itself cooperates with the securing piece51a.

The intermediate piece 50a cooperates with an additional adjustingelement 58. This adjusting element extends the intermediate piece so asto form a stop 54a which will cooperate with the half moons 55a and stop53a for holding the end 40 in position. The half moons 55a includecollars 56a which cooperate with a groove 57a.

The space 59 between the casing 35 of the protective device 7 and themeasuring probe 4 must include an electrically non conducting element,whereas the mud present in the environment in which the probe is to beused is generally conducting. It is then advisable to provide a systempreventing the introduction of mud into space 59.

Thus, for example, this free space 59 may be filled with an electricallynon-conducting liquid, such as distilled water or oil. In this case, noopening should be provided at the lower part of the probe, moreespecially so as to prevent the isolating liquid from escaping. However,in order to allow filling and emptying of this liquid, plugs 60 and 61are provided respectively in the embodiment shown in FIGS. 5 and 6.

In addition, in FIG. 6, a seal 62 is provided.

At the upper part of the protective device is provided an opening 363(FIGS. 5 and 6) so as to maintain the spacers situated on each side ofcasing 35 at the same pressure.

Such an orifice may serve for filling the free space 59.

Moreover, this orifice may be replaced by a flexible membrane, so as tomaintain the pressure balance on each side of the casing, while avoidingany exchange between the fluid occupying the free space 59 and theoutside environment.

FIGS. 7 and 8 illustrate two other embodiments relating to probes formeasuring the focused resistivity of geological formations. Some of thefocused resistance measurements are grouped under the name of"Laterolog".

In the case of FIGS. 7 and 8, probe 4 has in a way which is in no wiselimiting, three annular electrodes 26, 27 and 28.

In the case of FIG. 7, the probe is not extended by a lower tubularelement, as is the case for FIG. 8. Thus, in the case of FIG. 7, thecasing of device 7 includes the whole of the lower end 63 of probe 4.

The portion 64 of casing 65 of device 7, which is situated in thevicinity of the active zone of probe 4, is made from an electrically nonconducting material. This portion has annular electrodes 261, 271, and281, respectively, analogous to electrodes 26, 27 and 28.

The electric connection between the electrodes of probe 4 and theelectrodes of the protective device may be provided by means ofconducting rings 262, 272 and 282 and conducting studs 66.

Rings 262,272 and 282 may be secured to the electrodes of the probe asshown above in connection with FIG. 2 or 11.

FIGS. 10 and 11 show one embodiment of conducting studs 66 which arescrewed into the electrodes 68 of the protective device and/or of thecasing 67 of this device. Studs 66 thus screwed in come to bear againstthe conducting rings 15 and provide the electric continuity betweenelectrodes 69 of the probe and 68 of the protective device.

When the free space between casing 65 and probe 4 is not filled with anon-conducting material, as is the case for FIGS. 5 and 6, it is thenadvisable to insert non-conducting rings 70 and 71 between theelectrodes so that there are only small amounts of current passing fromone electrode of the probe 4 to the other.

In the case of FIG. 7, the amount of current passing directly fromelectrode 26 to electrode 27 is due solely to the clearance 72 existingbetween the non conducting rings 70 and the portions 64 of casing 65.

This amount of current is small, since clearance 72 in FIG. 7 is small.

When the ends 63 and 73 of the probe are conducting and serve forcollecting the return current, non-conducting rings 74 and 75 should beinserted between the endmost electrodes 26 and 28 and the conductingends 73 and 63 of the probe.

In the case of FIGS. 7 and 8, the parts of the casing 65 opposite theconducting ends 73 and 63 of the probe are made from an electricallyconducting material.

Of course, these parts, which may be made from metal, only begin beyondthe non-conducting rings 74 and 75.

The embodiments illustrated in FIGS. 7 and 8 have an orifice 84, at thelow part, which allows the mud in the well to pass upwardly within thecasing 65 and may also include an orifice (not shown) in the upper part.This orifice may be identical to that 363 of FIGS. 5 and 6.

Reference numeral 85 designates a spring providing a direct connectionbetween the conducting part 77 of the casing and the conducting end 63of the probe.

With such an assembly, the space between the non conducting rings 75,the conducting parts 77 and the end 63 of the probe may be filled with anon-conducting material.

The ends of the protective devices shown in FIGS. 7 and 8 may be fixedto probe 4 in the same way as in FIGS. 5 and 6.

Nevertheless, in the case of FIG. 8, the seal 62 may be omitted;

In fact, in the embodiment shown in FIG. 8, it is not necessary toisolate the filling fluid from the surrounding environment in which thedevice of the operation is to operate.

FIG. 8 includes several variants of construction of the protectivedevice. In a first variant, the non-conducting rings are of greatthickness and may even have a thickness equal to the distance separatingtwo successive conducting rings 262 and 272, as is the case for ring 78.

Furthermore, it is possible to position and hold the different rings,conducting or not, in position by means of a stack of spacers and ringsas is shown in FIG. 8. The spacers 79, 80 and 81 shown in this Figureserve for holding rings 75, 282 and 71 in position.

It is obvious that in this case it is advisable to dispose means forholding and/or positioning the spacers, either on the probe 4, or on thecasing 65 of the widener. It is this latter case which is shown in FIG.8 where the forces exerted on spacer 79 are transferred to casing 65through the stop 82.

The forces exerted on the isolating ring 83 of FIG. 8 may be transferredto the probe by the ring 83 itself.

Spacer 79 of FIG. 8 at the conducting end 63 is also conducting, so asto allow the return of the electric currents.

Of course, if this spacer had been electrically non conducting, theconducting part 77 should have been in direct contact with theconducting end 63 of probe 4, for example, through the bearing surface86.

FIG. 10 shows a particular embodiment of the conducting rings 15. Infact, they are enchased between two layers of isolating material 86 and87. The assembly thus obtained completely isolates electrode 69.

In such an embodiment, the non conducting rings situated on each side ofthe conducting ring 15 are therefore formed by non conducting materiallayers 86 and 87.

In the case of FIG. 11, the conducting ring 15 is enchased by thickspacers 88 and 82 which also provide the non conducting ring function.

In FIGS. 10 and 11, the height of the electrodes 68 of the protectivedevice is substantially the same height as the electrode 69 of theprobe.

FIG. 9 illustrates the case of a probe making focused resistivitymeasurements and induction measurements.

In this case, the probe should be placed in an environment whichconducts electricity as little as possible. This is why casing 90 issealed in the same way as casing 35 of FIG. 5. Thus, this protectivedevice is made from a non conducting material and includes a plug 60, asdistinct from the embodiment of the device shown in FIG. 5.

Casing 90 includes electrodes having the form of inserts 161a, 161b,161c, 161d . . . , as shown in FIG. 13. It should be noted that thearrangement shown in FIG. 13 applies not only to the case of FIG. 3 butalso to that of FIG. 9, since the probe illustrated in FIG. 3 is of thesame type as that illustrated in FIG. 9.

The difference between these two embodiments resides in the fact that,in the case of FIG. 3 the device is formed of a solid assembly, whereasin the case of FIG. 9 the device includes a casing 90 and centeringrings 91, 92, 93 when moreover the space between casing 90 and probe 9may be filled with an insulating liquid such as distilled water or oil.

The insert electrodes 161d are disposed and connected together in thesame way as shown in connection with FIGS. 3 and 13.

Preferably, a single electrode 16a from each row 16 is connected to aninsert electrode 161d of the row of analogous electrodes situated on theouter wall of the device.

This connection is shown in detail in FIG. 12, reference 16a designatingthe inset electrode integral with probe 4. Reference 161d designates theinsert electrode situated on the outer wall of the device.

This insert has a screw thread 94 which cooperates with a tapping 95formed in the casing 90 of the device. Moreover, this insert includes ahousing 96 in which is placed a spring 97 at the end of which is placeda contact 98.

Spring 97 has a length such that when the insert 161d is screwed ontocasing 90, it maintains the electric connection between inserts 16a andcontact 98, thus forming a pusher.

Of course, the embodiment illustrated in FIG. 9 requires angularpositioning of device 7 relatively to probe 4, which positioning may beprovided by any known means.

Furthermore, the widener shown in FIG. 9 may be adapted at its lowerpart in the same way as illustrated in the lower part of FIG. 6 so thatthe probe 4 of FIG. 9 may be extended by an additional element, moreespecially a tubular element.

FIG. 14 illustrates a probe 101 or a sensitive part of a probe having acover 102 protecting this probe more particularly from longitudinal(traction or compression) and transverse and twisting actions existingbetween an upper element 103 and a lower element 104 connectedrespectively to the upper and lower parts of probe 101.

These lower and upper elements may be those of a drill pipe string orother parts of the probe little or not at all sensitive to twisting orelse other probes included in a probe string.

Mechanical stresses such as those caused by traction or compressionforces may for example occur in the use of the devices and methodsdescribed in the patents: U.S. Pat. Nos. 4 457 370; 4 570 709; FR-A-Nos.2 547 861; 2 544 013 or FR-A-No. 2 564 894.

The cover is fixed to the ends of the probe by two fixing members 105and 106 which cooperate respectively with two grooves 107 and 108 placedat the ends of the probe.

The first 105 and the second 106 of these two fixing members eachinclude an arresting element, such as a system of two half moonsrespectively 109, 110 cooperating with the first 107 and the second 108groove and forming a first and a second collar relatively to the outersurface of probe 101.

A first assembly of fixing pieces which enchases the first collar bylocking it includes an intermediate piece 111 and an end part 113 andforms two stops adapted for cooperating with this first collar. Byencasing the arresting member is meant the fact that the securing piecessurround the arresting member while preventing its escape.

A second assembly of securing pieces which is adjustable and whichencases the second collar by locking it includes an intermediate piece112, an end part 114 and an adjustment piece 116 and forms two stopsadapted for cooperating with this second collar.

The first and second fixing members 105, 106 are held against rotationwith respect to the probe by means of screws 115 and 118 fastening thefixing pieces together and whose ends (of these screws) each cooperatewith studs 117 and 120 placed at the upper and lower ends of the probe.

Between each of these two existing members 105 and 106 is screwed, bymeans of two threaded portions 123 and 124, a protective casing 122which is immobilized on these members by a series of screws 125 and 126,adapted for preventing twisting between the lower 104 and upper 103elements and adapted to transmit the twisting forces between them.

If it is desired to seal the cover 102, seals 127 and 128 may be placedin the intermediate pieces 111 and 112 to balance the pressures betweenthe inside and the outside of the cover through an orifice 129. Thecover may include windows adapted for the operation of members such asanchorage arms, probe detector.

Of course, the cover will be adapted for transmitting the signalsemitted or received by the probe without too much damping and theinfluence of this cover on the measurements made by a probe will beknown so as to allow correct calibration of the probe.

The cover may be adapted so as to protect the probe or the instrumentfrom certain mechanical actions only. Thus, for example, the cover maybe adapted for protecting the probe solely against traction andcompression forces.

What is claimed is:
 1. A protective device for a logging probe having alongitudinal axis and having an exterior surface with a small diameterrelative to a well in which the probe is to operate, said devicecomprising a rigid tubular-like casing adapted to be connected to theexterior surface of the probe and acting to enlarge the effectivediameter of the exterior surface of the probe in comparison with thewell diameter, fastening means for locating said rigid casing coaxiallyon the probe and for fastening the casing circumferentially around theprobe on at least one level of said exterior surface of the probe, saidrigid casing having an exterior surface longitudinally surrounding atleast the exterior surface of the probe arranged around an active partof said probe for carrying out the logging measurement, said casingbeing capable of transmitting a signal emitted and/or received by saidprobe without substantial attenuation on the signal, wherein theexterior surface of the casing is spaced from the exterior surface ofthe probe and from the active part of the probe thereby enlarging theeffective diameter of the probe and the fastening means for the casingare located on the probe so that mechanical stresses occurring in thewell are applied and transmitted along the exterior surface of saidcasing without adversely acting on the exterior surface of the probearranged around the active part of said probe.
 2. A protective devicefor a logging probe according to claim 1, wherein said casing has anexterior wall which defines said exterior surface and which is spacedfrom the exterior surface of the probe, said exterior wall and saidprobe defining a sealed space around the active part of said probe.
 3. Aprotective device for a logging probe according to claim 2, wherein saidsealed space is filled with an electrically non-conducting materialincluding distilled water or oil.
 4. A protective device for a loggingprobe according to claim 1, wherein the rigid casing comprises acentering means for positioning the casing coaxially with the probe. 5.A protective device for a logging probe according to claim 4, whereinsaid centering means comprise rings.
 6. A protective device for alogging probe according to claim 5, wherein said centering meanscomprise means for fixing said rings around the probe.
 7. A protectivedevice for a logging probe according to claim 5, wherein spacers arelocated longitudinally against the exterior surface of the probe formaintaining the position of the electrical connections and centering therings on the probe.
 8. A protective device for a logging probe accordingto claim 1, connected to an induction logging probe, wherein the casingsurrounds the active part of the probe so as to form a closed volumecompletely isolated of the well, without attenuation of a signal emittedand/or received by said probe.
 9. A protective device for a loggingprobe according to claim 1, connected to a resistivity measurementlogging probe.
 10. A protective device for a logging probe according toclaim 1, wherein said casing has an exterior wall that is adapted forwithstanding lateral and axial stresses of compression and traction, andtorsion mechanical actions, without transmitting said stresses to theactive part of the probe.
 11. A protective device for a logging probeaccording to claim 1, connected to a probe for combining resistivity andinduction measurements wherein said probe includes electrodes in theform of inserts located around the circumference of the probe and aroundthe casing, on different planes perpendicular of the probe, a singleelectrical connection being placed in a plane between an insert of theprobe and an insert of the casing.
 12. A protective device for a loggingprobe according to claim 1, wherein said casing comprises at least oneelectrically non-conducting dividing wall between an exterior surface ofthe casing and the exterior surface of the probe, said wall beinginserted substantially perpendicular to the probe between two planes,said wall comprising electrodes of the probe, electrodes of the casingand electrical connection means.